1. Statement of the Technical Field
The present invention relates to heat sinks and more particularly to a method and apparatus of securing a heat sink above a central processing unit (CPU) of a computer in order to divert the weight and force of the heat sink to the computer's chassis or mounting plate rather than toward the CPU while maintaining the requisite thermal interface with the CPU.
2. Description of the Related Art
Heat sinks are a vital part of any computer system. The heat generated by continued and extended use of a computer can severely damage the electrical components in the computer. Heat sinks provide a way for the heat to be transferred away from the source and away from critical components. To increase the amount of thermal transfer, heat sinks typically include a large surface area or a large number of thermally conductive fins. However, the problem that arises when large heat sinks or heat sinks with a large number of fins are used is that critical space within the confines of the computer chassis is used up. Also, heavy heat sinks must be secured directly to the computer chassis in order to avoid transmitting the direct weight of the heat sink on the CPU.
The contact area between the heat sink and the electrical components and the pressure at the point of contact between the heat sink and the heat source are also important considerations in heat sink design. A heat sink with a flat contact area is preferred since a thinner layer of thermal compound may be used. This reduces the thermal resistance between the heat sink and the heat source. The pressure between the heat sink and the heat source must be high in order to maintain the requisite thermal contact and to facilitate thermal flow. Mechanical clips may help maintain the requisite pressure between the surface of the heat sink and the CPU, but such clips are usually difficult to install and are not reliable when the computer is being shipped. Even a slight jarring during shipping may cause the weight of the heat sink to fall directly on the CPU or motherboard causing severe damage. Further, because of the increased thickness in motherboards, the use of an under-the-board spring to dampen the force exhibited by the heat sink on the CPU and other electrical components is no longer feasible.
The recent proliferation of Land Grid Array (LGA) sockets have created another problem that must be considered during heat sink design and particularly in the manner in which heat sinks or other cooling devices are attached to the socket/CPU assembly. Current LGA socket designs frequently contain heat sinks as part of the assembly. The heat sink base is usually used as one of the loading plates in the assembly and is typically attached to a back-side stiffener using multiple screws or spring-loaded threaded fasteners. Even these simple attachment means can consume a significant portion of the effective heat sink volume, since the screws or spring-loaded fasteners protrude through the heat sink and require removal or partial removal of some of the fin structure, thereby reducing its thermal efficiency. Additionally, deflection that might occur under actuation load can create gaps between the heat sink and the assembly that can compromise the thermal effectiveness of the heat sink and/or cause the weight of the heat sink to fall directly on the CPU.
It is therefore desirable to have an apparatus and method that allows a heat sink to be mounted above a CPU and to deliver a load commensurate with the required thermal flow characteristics of the heat sink and to provide a mechanism to hold the heat sink firmly in place with the weight of the heat sink being transmitted to the chassis or mounting plate of the computer rather than the CPU, motherboard or other critical components of the computer.